Large-Gap Quantum Anomalous Hall Effect in Monolayer Halide Perovskite

We theoretically propose a family of structurally stable monolayer halide perovskite A${}_3$B${}_2$C${}_9$ (A=Rb, Cs; B=Pd, Pt; C=Cl, Br) with easy magnetization planes. These materials are all half-metals with large spin gaps over 1~eV accompanying with a single spin Dirac point located at K point. When the spin-orbit coupling is switched on, we further show that Rb${}_3$Pt${}_2$Cl${}_9$, Cs${}_3$Pd${}_2$Cl${}_9$, and Cs${}_3$Pt${}_2$Cl${}_9$ monolayers can open up large band gaps from 63 to 103 meV to harbor quantum anomalous Hall effect with Chern numbers of $\mathcal{C}=\pm 1$, whenever the mirror symmetry is broken by the in-plane magnetization. The corresponding Berezinskii-Kosterlitz-Thouless transition temperatures are over 248~K. Our findings provide a potentially realizable platform to explore quantum anomalous Hall effect and spintronics at high temperatures.